Individuals propel themselves on foot in a variety of ways including walking, running, and ascending or descending stairs or sloped surfaces. Gait may be assessed in terms of a gait cycle, also called a stride. A stride begins when a reference foot (either the left or right) makes contact with the ground and ends when it next contacts the ground. A stride requires three instances when one of the feet makes contact with the ground—two contacts by the reference foot and one contact made by the opposite foot. During the stride, the reference foot spends some time in contact with the ground (called stance) and some time apart from the ground and moving forward (called swing). Both swing and stance of each foot are required to move forward.
A stride is composed of two steps. A step is the action occurring in the interval from the moment that one foot contacts the ground to the moment when the other foot contacts the ground. Step duration is not simply the stance time of one foot. During a walking stride, some time may be spent with both feet touching the ground (called double limb stance) and during a running stride, some time may be spent with neither foot on the ground. Thus, the stance times of each foot may add to more than duration of a walking stride and/or less than the duration of a running stride.
A step may be attributed to either the left foot or the right foot, though actions of both feet are necessary to take a step. A step is often attributed to the foot that is off the ground and moving forward during the step interval. However, steps taken on a gait mat or other instrument may be attributed to the foot touching the mat at the beginning of the step interval.
Steps have attributes sometimes referred to as gait parameters. Step duration is one such parameter and is defined by the beginning and end points of the step. Step frequency is the number of steps taken within a given time period and is the reciprocal of the average step duration during the time period. Step length is the component of the distance between the contact points defining the beginning and end of the step that is in the direction the individual is moving. The walking speed of an individual may be calculated by multiplying step length by step frequency. (Walking, as used herein, may refer to any step-taking activity including, but not limited to, walking, running, ascending, or descending.) Step width is the component of the distance between the contact points that is perpendicular to the direction the individual is moving in the plane of the ground. (Ground, as used herein, refers to any surface on which an individual takes steps and includes, without limitation, floors, stairs, pavement, and natural terrains.)
The portion of a step in which an individual supports his or her weight on a single leg may be referred to as single limb support (SLS) and the portion in which weight is supported on both limbs may be referred to as double limb support (DLS). During DLS, weight may not be supported equally by the legs and DLS may be distinguished from double limb stance which refers to the portion of the step during which both feet are touching the ground. In contrast, when only one foot is in contact with the ground, weight is presumed to be supported by the grounded foot, so there is no need to distinguish between single limb support from single leg stance. The proportions of each step spent in DLS and SLS may be indicative of gait health. In particular, longer periods of DLS may indicate difficulty taking steps. Some gait analysts classify every moment in the gait cycle as either SLS or DLS while others have a third category for transition between SLS and DLS. Under either classification system, both SLS and DLS may be indicative of general health and gait health in particular.
Gait analysis has been used not only to document gait abnormalities but also to determine the underlying causes of the abnormalities and, in some cases, to recommend a treatment. Gait analysis has traditionally been performed in a gait analysis laboratory. Instruments used to perform gait analysis detect a variety of measures associated with walking. Sensor mats, for example, are mats with numerous pressure sensors on which subjects may walk. Sensor mats, in combination with appropriate analytical tools, may generate measures such as those discussed above. However, laboratory-based gait-measuring equipment tends to be expensive, requires that subjects travel to the laboratory, and observes subjects for only the limited time that they are present at the laboratory. The benefits of gait analysis would be available to more patients if it could be conducted using less expensive equipment and the conclusions drawn from gait analysis would be more robust if clinicians could observe patients outside of the laboratory over longer time periods.
In recent years, accelerometers have become smaller, cheaper, more accurate, and more energy efficient. An accelerometer may refer to a device that measures either linear or angular acceleration. However, accelerometers measuring angular acceleration may also be called gyroscopes, gyrometers, or simply gyros. An accelerometer may also refer to a device that measures acceleration in more than one direction. Triaxial accelerometers have three axes that are at least approximately orthogonal to one another. The output readings from accelerometers may be plotted over time and can be viewed as a signal.
While coupling an accelerometer to a user's hip or leg may yield informative data regarding gait, many users prefer wearing accelerometers elsewhere. Wrist-worn accelerometers have become popular among consumers and may allow for observation of data among a greater number of users and for a greater proportion of the day than accelerometers worn on the hip or leg. However, wrist-worn accelerometers present challenges with respect to inferring gait parameters from the acceleration data.